Employee and Agent Benefits (Details 6) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Pension benefits
Contributions
The low end of the range of possible contributions to be made during the next fiscal year to the qualified and nonqualified pension plans combined	$ 75
The high end of the range of possible contributions to be made during the next fiscal year to the qualified and nonqualified pension plans combined	125
Estimated Future Benefit Payments
Estimated future benefit payments, Year 1	83.2
Estimated future benefit payments, Year 2	92.0
Estimated future benefit payments, Year 3	96.0
Estimated future benefit payments, Year 4	101.4
Estimated future benefit payments, Year 5	107.4
Estimated future benefit payments, Years 6-10	632.5
Other postretirement benefits
Estimated Future Benefit Payments
Estimated future benefit payments, Year 1	20.1
Estimated future benefit payments, Year 2	21.1
Estimated future benefit payments, Year 3	22.2
Estimated future benefit payments, Year 4	23.0
Estimated future benefit payments, Year 5	23.9
Estimated future benefit payments, Years 6-10	127.9
Amount of Medicare Part D subsidy receipts
Medicare Part D subsidy receipts, Year 1	0.9
Medicare Part D subsidy receipts, Year 2	1.0
Medicare Part D subsidy receipts, Year 3	1.1
Medicare Part D subsidy receipts, Year 4	1.1
Medicare Part D subsidy receipts, Year 5	1.2
Medicare Part D subsidy receipts, Years 6-10	$ 6.6